1. Field of the Invention
This invention relates to the removal of fluids from wells, and more particularly concerns apparatus for retrieving water specimens under conditions which prevent alteration of the specimen.
2. Discussion of the Prior Art
The quality of naturally occurring water is a matter of increasing concern. Various toxic pollutant substances find their way into aquifer systems which may involve interconnected bodies of water such as lakes, rivers, bays and reservoirs. The toxic species may derive from industrial effluents, human wastes or natural factors of geological weathering, aging and erosion. The primary means of intercommunication of bodies of water within a single aquifer system is groundwater, namely water that flows underground at depths between about 15 and 150 feet.
In assessing the nature, cause and magnitude of pollution of an aquifer system, it is important to monitor associated groundwater at numerous sites. Because the characteristics of the groundwater usually varies with time, repetitive sampling is necessary.
Certain characteristics of water, such as pH, conductivity and redox potential can be monitored by detectors which provide continuous telemetering of data to a location remote from the monitored site. However, in most instances, more complete data is needed which can only be obtained by the grabbing of samples and transport of the samples to a full service analytical laboratory. In particular, the samples may be tested for toxic heavy metals by way of atomic absorption analysis, and toxic organics may be determined by way of gas chromatography/mass spectrometry analysis.
In order to accurately evaluate groundwater samples taken from a well, it is important to prevent changes from occurring in the water sample. The seemingly innocuous manipulation of pouring a water sample into a holding container can, for several reasons, destroy the validity of the sample. One of the involved reasons is that highly volatile species such as trichlorethylene and other low molecular weight carcinogens, dangerous at concentrations as low as 30 ppb, can quickly transfer from the water to the gas phase above the water. This is a partition effect, the rate and magnitude of which is governed by Raoult's law of physics. In the standard analytical procedure for volatile species, EPA Method SW846, it is stated in paragraph 4.1.2: "When collecting the samples, liquids should be introduced into the vials gently to reduce agitation which might drive off volatile compounds. Liquid samples should be poured into the vial without introducing any air bubbles within the vial as it is being filled. Should bubbling occur as a result of violent pouring, the sample must be discarded." Another undesired effect in the handling of groundwater samples is that oxygen from air may enter an otherwise anaerobic water sample.
Numerous techniques are known for the lifting of liquids such as water or oil from deep wells for sampling or production purposes. A number of such techniques involve the use of compressed gas. For example, U.S. Pat. No. 4,489,779 to Dickinson, et. al. discloses a gas-activated pump apparatus for withdrawing samples of groundwater from a well. The Dickinson pump employs a flexible bladder disposed within a valved housing. Sequentially pulsed expansions of the bladder drive water upwardly from said housing. U.S. Pat. No. 3,963,377 to Elliot, et. al. discloses a bladder-type pump somewhat similar to that of Dickinson. A complicating aspect of such bladder-type devices is that the pulsed expansions of the bladder require equipment components which permit expulsion of air from the bladder while creating a pressure differential between the interior of the bladder and the enveloping housing.
U.S. Pat. No. 5,004,405 to Breslin discloses a pump for use within a well casing, and employs a valved cylinder wherein compressed gas and liquid admitted to the top of the cylinder function as a piston to drive liquid in the bottom of the cylinder upwardly through a centered stored pipe. The compressed gas and liquid are in direct interfacial contact within the cylinder. U.S. Pat. No. 3,814,545 to Waters concerns a pump for delivering oil upwardly from a well, and utilizes a cylinder wherein a pressurized upper fluid of low density serves in piston-like manner in direct interfacial contact with the oil. The aforesaid pumps rely upon the hydrostatic pressure of the pumped liquid to fill a pumping chamber.
In certain sampling wells, particularly those of relatively shallow depth, there is insufficient hydrostatic pressure of the pumped water to achieve self-filling of a pumping chamber. In order to provide adequate driving force to transfer such water into a pumping chamber, an augmenting pressure gradient is needed such as may be produced by creating a negative pressure within the pumping chamber. However, if the water is exposed to a low pressure gas interface, volatile pollutants would escape from the water being sampled.
In order to remove meaningful samples from wells that have been stagnant for long periods of time, it is necessary to initially remove the stagnant water. Such removal often necessitates the pumping of large volumes of water. It is therefore desirable that any pump used for the accurate removal of sample quantities also has the ability to pump large volumes for disposal purposes.
It is accordingly an object of the present invention to provide a pump apparatus for the controlled delivery of water to above-ground elevation.
It is another object of this invention to provide a pump as in the foregoing object which accurately preserves the composition of groundwater for sampling purposes.
It is a further object of the present invention to provide a pump of the aforesaid nature which is actuated by a compressed gas but prevents direct interfacial contact of the gas with the delivered water.
It is a still further object of this invention to provide a pump apparatus of the aforesaid nature capable of augmenting hydrostatic forces in admitting groundwater into said pump.
It is an additional object of the present invention to provide a pump apparatus capable of handling large volumes of water for the disposal thereof, and small volumes of water for sampling purposes.
It is yet another object of this invention to provide apparatus of the aforesaid nature of simple, rugged construction amenable to low cost manufacture.
These objects and other objects and advantages of the invention will be apparent from the following description.